Address synchronizer

ABSTRACT

A synchronizer for the address counter of an on-the-fly print wheel has two photoelectric cells, one of which generates pulses in response to all character pads, or spaces, of the wheel, and the other in response to all spaces but one. The unpaired pulse is used for setting the address counter.

United States Patent Inventor Appl. No.

Filed Patented Assignee Beat A. Kocher Alameda, Calif. 754,431

Aug. 21, 1968 Mar. 2, 1971 The Singer Company ADDRESS SYNCHRONIZER 4 Claims, 14 Drawing Figs.

U.S. Cl.

Int. Cl Field of Search 250/219 (IDD), 231 (SE), 233; 197/53 References Cited UNITED STATES PATENTS Dumey Pfleger Davis et al. Doersam McLaughlin et a1 Thayer Kondur Primary Examiner-Edgar S. Burr Attorney-Charles R. Lepchinsky 101/93 101/93 101/93 101/93 101/93RC 197/53X 197/49 ABSTRACT: A synchronizer for the address counter of an onthe-fly print wheel has two photoelectric cells, one of which generates pulses in response to all character'pads, or spaces, of the wheel, and the other in response to all spaces but one. The unpaired pulse is used for setting the address counter.

Patented March 2, 1971 4 Sheets-Sheat l ATTORNEV Patented March 2,1971 3,566,782

4 Sheets-Shem z commo'suce I PRINT,

DETECTOR comm.

ADDRESS SYNCIIRONIZER BACKGROUND OF THE INVENTION 1.

SUMMARY OF THE INVENTION The system of the present invention is applicable to a spoked wheel, or the like, where a single signal per revolution is not readily obtainable. It utilizes a single difference between two trains of signals.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and advantages and objects will be apparent from the following description of a specific embodiment of the invention, reference being had to the accompanying drawings wherein:'

FIG. I is a partial perspective view of an on-the-fly printer embodying my present invention;

FIG. 2 is an enlarged detail of the apparatus of FIG. 1;

FIG. 3 is an elevation of part of the detail of FIG. 2;

FIG. 4 is an enlarged sectional view taken along the lines 44 of FIG. 2;

FIG. 5 is a partially schematic diagram of a logic and control system;

FIG. 6 is a graph showing waveforms illustrating part of the operation of the apparatus of FIG. 5;

FIGS. 7, 8, 9 and 10 are two views, a diagram, and a graph similar to FIGS. 2, 3, 5 and 6 for showing a modified construction;

FIG. 11, 12 and 13 are a view, diagram and graph similar to FIGS. 3, 5 and 6 for showing another modification, and

FIG. 14 is a view similar to FIG. 3 of a further modification.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a print wheel 10 having 64 regularly spaced character pads, indicated generally at 22, each carried on the end of a radial, flexible spoke 20. The wheel rotates counterclockwise continuously, for example, at 900 revolutions per minute, and a hammer l2 strikes the individual character pads 22 for printing on a work sheet 14 carried on a platen" 16.

A photoelectric assembly 18 includes two photoelectric cells 24 and 26, which are also shown in FIG. 2 and 3, and includes also cooperating light sources 25 and 27 which, as shown for cell 26 in FIG. 4, provide narrow beams of light through which the character pads pass successively. Thus, the pads and the spaces between them provide dark and light elements to which the photoelectric cells respond. One character pad 64- is radially shorter than the others. The photoelectric cell 24 and its cooperating light source 25 are set radially inward so as to respond to all 64 of the character pads of the wheel. Photoelectric cell 26 and its cooperating light source 27, FIG. 4, are set radially outward so that its light beam is not intercepted by the short character pad 64, but is intercepted by the other 63 character pads. Because of space limitations, the two cells 24 and 26 cannot respond simultaneously to the same or adjacent character pads. Because of space limitations, the two cells 24 and 26 cannot respond simultaneously to the same or adjacent character pads. In this construction of FIGS. I to 6 they are spaced circumferentially, as shown in FIG. 3, so that the trailing edge of a pad is aligned with cell 24 when the centerline of another pad is aligned with cell 26.

As is shown best in FIG. 3, the character pads 22 are wider than the spaces between them so that the photoelectric cellsare darkened by each pad longer than they are illuminated through each space between pads.

As shown in the diagram of FIG. 5, in a known manner, a coder 30 receives an input signal identifying a character to be printed and transmits a number representing the address of that character to a coincidence detector 32. A continuously running, address counter 34, driven by pulses from the photocell 24, presents, in succession, the numerical addresses of the characters on the print wheel, and when an address so presented corresponds to the address of the character to be printed, a signal is transmitted to the print control 36 which actuates the hammer 12 (FIG. 1) for printing the desired character.

The present invention provides the necessary synchronism of the counter 34 with the rotation of the wheel 10.

The pulses, or signals, from the photoelectric cell 24 are paired by the pulses, or signals, from the photoelectric cell 24 are paired by the pulses, or signals, from the photoelectric cell 26 except at the passage of the short character pad 64. The

failure to pair this one signal from the cell 24 identifies the specific instantaneous position of the wheel 10, and is utilized for setting the address counter 34 to a particular numerical address, such as 64.

Certain waveforms appearing in the system are shown in FIG. 6. There, the curves 40 and 4,2 depict the output of photoelectric cells 24 and 26. The other curves depict voltages in the circuits of FIG. 5. For convenience, the values of these curves will be described in relative terms. The highvalues will be called positive," that is, positive relative to the others, and the low values negative, negative to the others.

Conveniently in FIG; 5, the counter 34 counts consecutively from I to 64. Each number so counted constitutes the identification, or address, of one of the character pads 22 and, conveniently, the short pad 64 has the address 64" In FIG. 6 the curve 42 is labeled with the numbers 62, 63, 64 and 1 to indicate the addresses of the particular pads passing the photoelectric cell 26. Asshown by this curve, the cell 26 generates a dark value, signal, or pulse, at each pad except the pad 64. The signal represented by the curve 40 from the photocell 24 is similar to the signal 42, but has dark pulses at all character pad positions. Because the photocells 24 and 26 are spaced apart, as shown in FIG. 3, the dark pulse produced in photocell 26, for example, by the pad 62 as shown by curve 42, is accompanied by a light-going-change produced in the photocell 24 produced by the trailing edge of a different pad. but these signals will be described here with respect to the pad numbers marked on the curve 42.

, In FIG. 5, the signal C from the photoelectric cell 24, shown by the curve 40 in FIG. 6, is applied to a level-responsive NAND gate 44, FIG. 5, operating as an inverting amplifier, to produce the signal G which is shown by the curve 47 in FIG. 6.

The signal G is applied to a second NAND 45 for producing the signal B, shown by the curve 48 in FIG. 6. This signal B is applied as a clock signal for driving the address counter 34, and also for triggering a delay flip-flop 50.

The signal H from the photoelectric cell 26, shown by the curve 42 in FIG. 6, is applied to NANDs 52, operating as a noninverting amplifier, for producing the signal D, shown by the curve 53in FIG. 6. The signal D is applied as the state-controlling, or data, input to the flip-flop 50. The output 0 from the flip-flop 50 and the signal G from the NAND 44 are applied to a NAND gate 55 for producing a synchronizing signal S which is applied to the address counter 34 for resetting it, as will be described.

The flip-flop 50 is a" delay-type," edge-triggered flip-flop, which is quiescent at all times except when a negative-going signal is applied to it for triggering it, as, for example, in response to the negative-going swings of the signal B of FIG. 6 at the times indicated by the vertical lines 57 and 58. Upon the occurrence of such a triggering signal, it stays in, or changes to, the state that makes its output Q opposite to the value that the data signal D had at the time the triggering signal was ap plied. This operation accords with the following truth table: At

time of negative-going trigger signal B signal D Q Q As shown in FIG. 6, the signal C consists of a series of dark pulses, or positive pulses, such as 70, each produced by the movement of one of the character pads 22 past the photoelectric cell 24, FIGS. 2 and 3. The signal G and B both follow the signal C but have opposite phases. The negative-going swing of the curve B at, for example, the swing 71 in FIG. 6, occurs in response to the light-going, or negative-going swing of the curve C, as at 72 in FIG. 6, as the photoelectric cell 24 FIG. 3, is being uncovered by one of the character pads 22.

The H and D signals, shown by the curves 42 and 53in FIG. 6, have dark, or positive, pulses such as 74 and 75. These dark pulses begin earlier and end later than the negative-going swings, such as 71, of the curve B.'In particular, the negativegoing B signal is bracketed in time by the dark, or positive, pulses of the D signal.

At the one rotated position of the wheel 10, FIG. 2, in which the short character pad 64 is passing the photoelectric cell 26, the dark pulse is missing from the H and D signals, as shown at 77 and 78 in FIG. 6, where the missing pulses have been sketched in dotted lines.

The flip-flop 50, FIG. 5, is controlled by the B and D signals, FIG. 6. The negative-going swing of the B signal, as at 71, determines the time that the D signal is to be responded to, and the level of the D signal determines the state that the flipflop 50 will stay in, or change to, at the time 71. The positive pulse 75 of the D signal in FIG. 6 is produced by the passage of character pad No. 62 past the photoelectric cell 26, so that the output Q of the flip-flop 50, shown by the curve 80 in FIG. 6 stays at a negative value. The operation is the same as the character pad No. 63 passes photoelectric cell 26, FIG. 2. Because character pad 64 is short and fails to darken the photoelectric cells 26, the curve D has a negative value 78 at the 64" position. Accordingly, the negative-going swing of curve B occurring at the time indicated by the vertical line 57 in FIG. 6, occurs during this negative value 78 of curve D and causes the flip-flop 50 to change state, so that its output 0 goes to the positive value indicated at 81 in FIG. 6. The next negative-going swing of the B signal occurs at the time indicated by the vertical line 58 in FIG. 6, at which time character pad No. 1 darkens the photoelectric cell 26 so that the D signal is at the positive value indicated at 83 to cause the Q signal to return to its negative value, shown at 84 in FIG. 6.

As best seen in FIG. 5, the signals Q and G are applied to the NAND gate 55. When these two input signals are positive, the output signal S of the gate 55 is negative. These two signals are both positive only during the interval between the two times indicated by the vertical lines 57 and 59 in FIG. 6. Consequently, during this interval the S signal goes negative, as shown at 85 in FIG. 6, and this negative signal resets the counter 34 to the count 64.

Because the two photoelectric cells 24 and 26 (FIGS. 2 and 3) respond to different parts of the print wheel 10, any nonuniformity in the sizes and spacings of the character pads, or vibrations of the pads on their spokes 20, can introduce irregularities in the relative timing of the negative swings, such as 71, in the signal B shown in curve 48, and the dark pulses such as 75 in the signal D shown in curve 53. Therefore, it is desirable that the dark, pairing pulses 75 bracket the negative swings of the B signal with considerable margin.

The signal B for driving the counter 34, FIG. 5, may not be needed at the position of pad 64, either because the counter is always brought to address 64" by the synchronizing signal S, or because the pad 64 will not be used for printing. In such a case, the counter 34 can be driven from either of the photocells 24 or 26.

after that trigger col-- FIGS. 7 to 10 disclose a second construction embodying my invention. There, a print wheel 90, similar to the print wheel 10 of FIG. 1, has a similar photoelectric cell 26 responding to all the character pads except a short character pad 640 for producing an I-Ia signal shown by the curve 91 of FIG. 10. This signal consists of an interrupted train of wide positive, or dark, pulses 92, with the dark pulse omitted at the position 640, corresponding to the passage of the character pads 64a past the photoelectric cell 26. A photoelectric cell 92 and its cooperating light source 93 are positioned to respond to the passage of the spokes 20, for producing a Ca signal, shown in FIG. 10 and consisting of a train of short positive, or dark, pulses 94. If desired, the spokes may be widened, as shown at 95, FIG. 8, to increase the obstruction offered to the light beam. A large diameter light beam increases the photoelectric sensitivity of the system, but the large beam also requires a broad spoke to completely obstruct it. Further, as will be described, it is necessary that the spokes be narrow enough that the pulses of the Ca signal be narrower than those of the Hi: signal.

The two photoelectric cells 26 and 92 must be spaced circumferentially of the wheel and integral number of spoke intervals, here shown as two intervals, so'that the dark pulses produced by the two photoelectric cells wild occur together in pairs. Thus, in FIG. 10, the short dark pulses 94 of the Ca signal are substantially centered on, and bracketed in time by the broad dark pulses 91 of the Ha signal.

As is shown in FIG. 9, the Ca signal from photocell 92 is applied to a pair of NANDs 101 operating as a noninverting amplifier for producing a Ba signal shown in FIG. 10, which is applied as a clock signal for driving an address counter 34 and is applied also to a NAND gate 103. The Hasignal from the photocell 26 is applied to a signal NAND 102, operating as an inverting amplifier for producing a Da signal, shown in FIG. 10, which is also applied to the NAND gate 103. The output S of gate 103 constitutes a synchronizing signal which is applied to the address counter 34 for resetting it.

In FIG. 10, the short dark pulses 97 of the Ba signal are positive, just as are the dark pulses 94 of the Ca signal. However, the long dark pulses 98 of the Da signal, because of the inversion by the amplifier 102 are negative. Thus, except at the position of the pad 640 marked on the Ha curve, the short, dark, positive pulses 97 of the Ba curve are paired and bracketed by the long, dark, negative pulses 98 of the Da curve, so that the two input signals to the NAND gate 103, FIG. 9, are not both positive at the same time. However, at the position of the short character pad 64a the dark pulse is omitted from the Da signal, and at this position the two signals Ba and Da are simultaneously positive to produce a negative pulse 99 in the 5a, or synchronizing, signal. This Sa signal is applied to the address counter 34, FIG. 9, for resetting it to a particular count such as 64" The system of FIG. 7 to 10 is somewhat simpler than that of FIGS. 1 to 6, but it imposes stricter limitations on the time of occurrence, and on the duration of, the pairing and bracketing pulses of the interrupted train of the Ha signal. The pulses 97 which must be bracketed in FIG. 10 are of greater duration than the negative-going switch 71 and in the B signal in FIG. 6.

FIGS. 11 to 13 disclose a third construction embodying the invention. As shown in FIG. 11, the two photoelectric cells 26 and 114 are spaced apart an integral number of half spaces, here shown as 2 spoke intervals, so that the dark condition of one cell will be accompanied by, or paired by, a light condition of the other. The cell 114 is spaced radially inward so that it responds to all of the character pads for producing a continuous train of pulses, or signals, and the photocell 26 is spaced radially outward so that it is darkened by all character pads except the short character pad 64 b so as to produce an interrupted train of pairing pulses or signals.

The signal Cb from the photoelectric cell 114 shown by the curve 116 in FIG. 13, is applied to a level-responsive NAND gate 118, FIG. 12, operating as an inverter, to produce the signal Bb which drives the address counter 34. As is shown in the graph of FIG. 13, the changes in the value of the Bb signal in curve 119 occur near the midlevel of the signal Cb in curve 116. Similarly, the output of the photoelectric cell 26 is applied to a NAND 120 operating as an inverting amplifier for producing the signal Db as shown by the curve 121 in FIG. 13. These two signals, Bb and Db, are applied to a NAND gate 123 for generating the synchronizing signal Sb shown by the curve 124 in FIG. 13, which is applied to the counter 34 for synchronizing it.

The output of the NAND gate 123 is negative when both of its inputs are positive, and is positive at all other times. It is convenient to view the signal Bb, shown in the curve 119, as consisting of short positive pulses, such as the pulse 126. Each of these corresponds to a short negative pulse in the signal Cb, as shown by the curve 116, and is produced when the open space between the character pads passes the photoelectric cell 114, FIG. 11. Thus, the pulse 126 may be viewed as a short, light pulse. Similarly, the signal Db shown by the curve 121, is conveniently viewed as consisting of long, negative pulses, such as the pulse 127, each of which is produced by a positive, or dark pulse, of the signal I-Ib shown in the curve 117. It is to be noted that the long negative pulses 52 bracket the short pulses 51; that is, they begin earlier and end later. Consequently, as long as the pulses of the trains 119 and 121 are paired, the two signals Bb and Db are not positive at the same time, and, consequently, the synchronizing signal Sb remains positive.

At the print wheel position shown in FIG. 11, the short character pad 64b fails to cover the photoelectric cell 26 and so fails to produce a dark pulse. This is the condition indicated by the position 64b marked on the curve Hb in FIG. 13. The omitted dark pulse is shown in dotted lines at 129 on curve 117, and at 130 on curve 121. Thus, at this 64b position of the print wheel, FIG. 11, the light pulse 132 of the Bb signal shown in curve 119, is unpaired by any dark pulse in the Db signal shown in curve 121, so that under this one condition, the Rb and Db signals have simultaneous positive values, and the gate 123, FIG. 12, passes the negative pulse 133 shown on the Sb curve 124 in FIG. 13. This synchronizing pulse goes to the address counter 34 for resetting it to the count or address 664-,

In the Db curve 121 of FIG. 13, the negative, or dark excursions, such as 127, are the signals or pulses pertinent to the operation of the device, even though their duration exceeds considerably the spaces between them. The length of time between these pulses can vary considerably.

In the construction of FIGS. 11 through 13, the character pads 22 are of such width compared to the spaces between them that the dark pulses produced by the pads are longer than the light pulses produced by the spaces. FIG. 14 shows a construction in which the present invention is applied to a print wheel in which the spaces between the pads produce longer pulses than do the pads themselves.

In FIG. 14 all the character pads of the wheel are full length, but the pads 63c and 64c are connected by a bridge 140 that closes the inner half of the light space between them. An outer photoelectric cell 142 receives a short dark pulse at each of the character pads, and an inner photoelectric cell 144 receives a long light pulse at each interpad space, except at the space closed by the bridge 140.

It is necessary that the pulses, or signals, of one of the two trains of signals be shorter, as the C signals in the described embodiments, and that the pulses or signals of the other train should pair the short signals and should bracket them in time.

Further, it is the train with the longer, bracketing signals, or pulses, that should be interrupted, that is, should omit pulses for indicating the rotated position of the wheel.

When a square wave, such as the B signal, in FIG. 6, is generated from a wave with less abrupt changes in value, such as the C curve of FIG 6, as the intensity of the light supplied to the photoelectric cell increases, the light pulses widen and the dark pulses become narrower. In the constructions of FIG. 11 and 14, where a train of light pulses is paired by a train of dark pulses, or visa versa, a change in light intensity changes the relative lengths of the pulses in the two trains. Accordingly,

where such light variations must be tolerated, the constructions of FIGS. 3 and 8 are to be preferred.

The system of the present invention operates reliably at all speeds of the print wheel from near zero speed to far above the intended operating speed, and furthermore puts the address counter 34 into synchronism with the print wheel at the very first passage of the omitted pulse element (the short character pad 64 in FIG. 2 or the bridge in FIG. 14). Thus, only during startup will the address counter 34 normally remain out of synchronism with the print wheel, and then for nor more than one turn of the wheel.

It will be apparent that the invention is capable of modifications and variations within the scope of the claims.

I claim: 1. A synchronizer for an address counter in an on-the-fly printer comprising, in combination:

first photoelectric means for generating a train of first signals;

second photoelectric means for generating an interrupted train of second signals for pairing with said first signals;

each interruption of said train of said second signals leaving a signal of said first train unpaired;

third means responsive to each such unpaired first signal for applying a synchronizing signal to the address counter of the printer; and

said signals are pulses, and each said second signal begins earlier and ends later than the first signal of the first train that is paired therewith.

2. The combination of claim 1 wherein the printer has a plurality of separate, radially-extending circumferentially spaced character pads, the pads and the spaces between pads present alternate light transmitting and light blocking paths to said photoelectric means, said third means includes a delay flipflop to which said first signals are applied as triggering signals, and to which said second signals are applied as date inputs; and wherein said flip-flop is triggered by the passage by said photoelectric means of an edge of a character pad.

3. The combination of claim 1 wherein the printer has a plurality of separate, radially extending, character pads, and the pads and the spaces between them present alternate light transmitting and light blocking paths to said photoelectric means, and wherein said first and second photoelectric means are spaced apart circumferentially of said wheel so that said first photoelectric means responds to a light transmitting path while said second photoelectric means responds to a light blocking path.

4. The combination of claim 1 wherein the printer has a plurality of separate character pads on'slender, radial spokes, wherein said first photoelectric means responds to said spokes and the spaces between them, and said second photoelectric means responds to said pads and the spaces between them.

Patent No.

Inventor(s) Beat A. Kocher Dated March 2, 1971 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column Column "lolumn line 25,

line 55,

lines 68,

delege "and objects";

change "FIG." to FIGS.

69 and 70, delete the entire sentenc beginning with "Because" it is a duplication.

lines 17 and 18,

line

line

line

line

line

line

line

line

line

line

line

delete "from thehphotoelectri cell 24 are paired by the pulses,

or signals, it is a duplication;

after "to" insert two delete this line; V

change "cells" to cell change "and" to an change "wild" to will change "Hasignal" to Ha signal change "switch" to swing change %spoke" to spoke change "64 b" to 64b change "nor" to not change "date" to data .mwd J n-a Signed and sealed this 30th day of November 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR.

1 Attesting Officer ROBERT GOTTSCHALK Acting Commissioner of Pat 

1. A synchronizer for an address counter in an on-the-fly printer comprising, in combination: first photoelectric means for generating a train of first signals; second photoelectric means for generating an interrupted train of second signals for pairing with said first signals; each interruption of said train of said second signals leaving a signal of said first train unpaired; third means responsive to each such unpaired first signal for applying a synchronizing sigNal to the address counter of the printer; and said signals are pulses, and each said second signal begins earlier and ends later than the first signal of the first train that is paired therewith.
 2. The combination of claim 1 wherein the printer has a plurality of separate, radially-extending circumferentially spaced character pads, the pads and the spaces between pads present alternate light transmitting and light blocking paths to said photoelectric means, said third means includes a delay flip-flop to which said first signals are applied as triggering signals, and to which said second signals are applied as date inputs; and wherein said flip-flop is triggered by the passage by said photoelectric means of an edge of a character pad.
 3. The combination of claim 1 wherein the printer has a plurality of separate, radially extending, character pads, and the pads and the spaces between them present alternate light transmitting and light blocking paths to said photoelectric means, and wherein said first and second photoelectric means are spaced apart circumferentially of said wheel so that said first photoelectric means responds to a light transmitting path while said second photoelectric means responds to a light blocking path.
 4. The combination of claim 1 wherein the printer has a plurality of separate character pads on slender, radial spokes, wherein said first photoelectric means responds to said spokes and the spaces between them, and said second photoelectric means responds to said pads and the spaces between them. 